1. Field of the Invention
The present invention relates to an image processing apparatus having a function to read original documents (images) (such as an image reading apparatus, document reader, copying machine, scanner or multifunction peripheral), image reading apparatus and document conveyance device.
2. Description of the Related Art
As an image processing apparatus equipped with a document reading function, an image processing apparatus that incorporates a so-called sheet-through type document reader that is fixed in place and reads the original document while the original document is conveyed thereover (Japanese Laid-Open Patent Applications H9-80647 and 2000-181152) has been proposed.
The image processing apparatus disclosed in Japanese Laid-Open Patent Application H9-80647 includes document conveyance rollers on the upstream and downstream sides of the document reader in terms of the direction of document conveyance. One roller of the pair of upstream document conveyance rollers can come into contact with and move away from the other roller, and control is carried out such that while the rollers are separated from each other before the trailing edge of the original document sheet is released from between the rollers, the next original document sheet comes into contact with the rollers before arriving at the document reader. However, in this image processing apparatus, because the state of the rollers is switched from ‘separated’ to ‘in pressure contact’ based on a document sheet feed signal, the trailing edge of the original document sheet that is being conveyed over the document reader may still remain between the upstream document conveyance rollers when the document sheet feed signal is output. Therefore, the original document sheet being conveyed becomes pressed between the upstream document conveyance rollers, and the fluctuation in load on the upstream document conveyance rollers that is generated at this time leads to a fluctuation in the load on the downstream document conveyance rollers that are pressing on the same original document sheet, resulting in a change in the document conveyance speed, which leads to a failure in reading of the original document sheet.
The image processing apparatus disclosed in Japanese Laid-Open Patent Application 2000-181152 includes document conveyance rollers on the upstream and downstream sides of the document reader relative to the direction of document conveyance. One roller of the downstream document conveyance roller pair can come into contact with and move away from the other roller, and when the leading edge of the original document sheet enters the area between the downstream document conveyance rollers, the rollers are separated from each other. However, according to this image processing apparatus, the problem arises that when the state of the rollers is switched from ‘separated’ to ‘in pressure contact’, the conveyance speed of the original document sheet being conveyed therebetween changes, resulting in a failure of reading of the original document sheet.